1. Field of Invention
The present invention relates to composite concrete structures. More particularly the present invention is directed to a multi-layered composite structure in which a high-tensile strength, liquid-impermeable imide layer is bonded to a steel-reinforced concrete layer.
2. Description of the Prior Art
The disclosed invention is a multi-layered composite structure, and a method for making same, which may be advantageously used to form bridge decks, roadway pavements, roofing decks, and the like.
Various materials, notably concrete, used in building construction and other civil engineering projects such as roads and bridges are susceptible to water penetration resulting either from inherent properties of the construction materials (e.g. porosity) or from imperfections (e.g. cracks) in the structures. Such imperfections in the structures may be caused by construction defects, or by deterioration of the structures over time due to harsh environmental conditions such as traffic and weather.
Reducing or eliminating water penetration through such structures is often desirable, particularly for below-grade building walls and for tunnels which permit passage of vehicular or pedestrian traffic under bodies of water. It is also often desirable to reduce or eliminate water penetration through roadway pavement and through bridge decking, because such water penetration may result in corrosion of reinforcing or supporting structural steel embedded in or adjacent to the pavement.
Concrete structures such as bridges, buildings and decks are typically reinforced with steel rebar, wire mesh, or coiled metal elements, for the purpose of providing the concrete structure with strength and rigidity. These concrete structures are expected to remain viable for many years despite the fact that they must withstand harsh environmental conditions. Corrosive agents are known to diffuse through concrete and to degrade reinforcing metals inside concrete structures, thereby reducing the strength of the structure. Chloride-containing compounds are among the most destructive corrosive agents to metal reinforcing materials.
Prior methods of protecting for example concrete roads from the adverse effects of through-concrete water migration have typically involved disposing an overlay comprising a waterproofing material such as latex or epoxy mixed with concrete on top of an underlying concrete base. This prior method has proven somewhat effective; however, two related problems detract from its usefulness.
First, the adhesive bond between the underlying concrete and the overlay is typically weak. When prior overlays (whether latex concrete or otherwise) are placed on an exposed surface of a cured concrete base, the achievable bond between the two layers is typically very weak.
Second, due to the difference between the thermal coefficients of contraction of the waterproofing material and the concrete base of prior pavements, and due the relative rigidity of prior cured waterproofing materials, cracks invariably develop between the adjacent pavement layers over time due to climatological temperature changes. Such cracks permit unwanted migration of water and corrosive agents between the layers and into the underlying concrete. Water trapped between the layers or within the underlying concrete renders the pavement susceptible to cracking and deteriorization due to stress concentrations in the pavement caused by expansion and contraction of the entrapped water as it alternatingly freezes and melts during periods of ambient temperature swings.
Another factor which contributes to the deterioration of the underlying concrete structure in prior pavement schemes is the relatively low tensile strength and inflexibility of the overlay. As a result of high localized stress concentrations caused by heavy traffic, overlays frequently break down over time, causing cracks to develop, and allowing water to permeate the underlying concrete.